This invention concerns improvements relating to the deposition of thin carboneous films.
Carbon thin films are very suitable for making surfaces abrasion-proof, smooth, or highly thermal conductive. Such a carbon film is deposited by use of chemical vapour reaction. A plasma state is developed in a reactive gas by applying high frequency electric energy between a pair of electrodes defining therebetween the deposition region, and by using a hydrocarbon gas and a carrier of hydrogen as the reactive gas a carbon film can be deposited on a surface. During the deposition process, positive ions, such as hydrogen ions, are impelled towards the surface to be coated by the voltage between the pair of electrodes and sputter the depositing film. This sputtering functions to reduce the formation of carbon bonds based on the sp and sp.sup.2 orbitals and to increase the proportion of carbon bonds based on the sp.sup.3 orbital, and as a result the carbon film tends to grow with a diamond structure.
Such prior art carbon films, however, have relatively high resistivities and therefore tend to collect on their surface electric charge which in turn attracts dusts. In case of the application of static electricity, charge is accumulated and undesirably kept on a protective film made of such a carbon film and as a result expected characteristics can not be maintained for a long use. The introduction of a conductive agent into the carbon film may resolve the problem. However, the conductive agent in turn creates absorption centers which place limitation to the application thereof.
On the other hand, such carbon films tend to be formed accumulating inner strain therein during the fabrication process. The inner strain sometimes causes peeling-off of the carbon film from the underlying surface. The problem seems to be solved by making thinner the films or providing an intermediate film between the carbon film and the underlying surface. However, the strength of such a thin film is not sufficient and the provision of such an intermediate film rises the production cost.